1. Field of the Invention
The present invention relates to environmental control systems for mass transit vehicles, such as aircraft, ships and trains.
2. Description of the Related Art
In the design and manufacture of mass transit vehicles such as transport aircraft, it is necessary to provide ducting for flow of gasses such as air through air conditioning systems leading to different locations throughout the fuselage. Depending on the rate of mass transfer and speed of flow, vibration transmission characteristics of the ducting and the surrounding frame structure, the noise emanating from the gas flow can be relatively loud, even to the point of distraction or irritation for crew members and passengers alike.
Constraints on design criteria for such environmental control system ducting stem from governmental and industrial regulations which focus on the safety of personnel in the event of a catastrophe such as an airplane accident or crash. These constraints include attention given to flammability, toxicity, smoke generation generated from vaporized combustibles. Furthermore, in the highly competitive nature of the aircraft industry, it is important such ducting be relatively economical and of a light weight so as not to heavily burden the overall weight of the aircraft or otherwise upset the balance of weight distribution throughout the fuselage.
It has been common practice to construct such environmental control system mufflers of non-metallic materials such as polyurethane and nylon with fiberglass batting as an acoustic absorbers. A typical muffler will incorporate a knitted sleeve placed on a tubular mandrel and over wound with steel wire and adhesively received together by polyurethane or silicone adhesives in what is termed a “wet winding” process. The external wall of such prior art mufflers typically consist of coated fabrics or films reinforced by winding a small cording of nylon or other polymer thereabout and adhering such cording by adhesive or heat sealing in the winding process. Closure caps are typically provided at the opposite ends of the muffler and are typically made from a rather complex lay up process using coated fabrics and adhesives.
The manufacture and assembly of such prior art mufflers is typically labor intensive requiring some degree of technical skills and is relatively time consuming thus driving up the cost of manufacture in an industry where the skilled labor is relatively expensive. In this regard, it is recognized that the addition of just one pound to the weight of an aircraft might add hundreds of dollars to the expense of operating the aircraft over its useful life. Additionally, for large jumbo aircrafts of present day design, just one aircraft might incorporate 100-200 or even more muffler devices.
Thus, there exists a need for a lightweight, low cost muffler apparatus which can be manufactured and assembled in a relatively economical manner and which will provide effective noise attenuation and provide a relatively low level of flammability, toxicity and smoke generation in the event of fire.